Thursday, October 23, 2014

Female Thyroid Cancer Rates near Nuclear Power Plants

I think this is my third post about the risk of living near nuclear power plants. Previous two posts on this topic are:
(1) Exposure to Radiation Causes Birth Defects or Abnormal Sex Ratioshttp://j.mp/Dangerous_Nuclear
(2) Infant Cancer Rates near Nuclear Power Plantshttp://j.mp/Infants_vs_NPPs

Now, let's go back to female thyroid cancer. The study I am citing here is two years old. But I think the results could explain the peculiar increase in thyroid cancer incidents in South Korea. According to the study:

In South Korea,
“Thyroid cancer incidence in women in the exposed and Control-1 was as high as 2.5 and 1.8 times, respectively, than in Control-2 cohort. And the trend in risk was statistically significant (p for trend = 0.03).” (Ahn et al., 2012)Note:
a. Exposed: the group living within a 5 km radius from the Nuclear Power Plants
b. Control-1: the inter-mediate proximity (5-30 km radius) group
c. Control-2: the far-distance (more than 30 km) group

It is NOT 2.5% or 1.8%, BUT 2.5 times and 1.8 times! If a woman is living within a 5 km radius from a nuclear power plant, she has 150% more possibility of getting thyroid cancer.

Thyroid cancer incidence among Korean females are definitely a serious concern. Let's see Table 1. Although the annual percentage change of overall cancer incidence was 5.4% over 1999-2011, that of thyroid cancer was unbelievably high 23.3%. If we are aware of the above study, researchers must find one of main causes of high thyroid cancer increase rate from the female patients' proximity to nuclear power plants.

Table 1. Trends in cancer incidence rates in females from 1999 to 2011 in KoreaUnit: Age-standardized incidence rate per 100,000

Although there is no statistically significant evidence about overall cancer incident rate and proximity to nuclear power plants, I suspect that presence of nuclear power plants could be a clue how to explain Korea's skyrocketing cancer mortality, as manifested in the figure below. While the average OECD countries showed 15% decline in cancer mortality rates during the past two decades, South Korea showed 6% increase. It was the 2nd highest increase rate in the OECD.

According to an IAEA data, South Korea has the most number of nuclear reactors per unit land area (Table 2). Korean people have more chance of finding themselves living near a nuclear power plants than any other country in the world. South Korea might urgently need a comprehensive re-examination of the relationship between people's proximity to nuclear power plants and other kinds of cancer.

Maybe some people will ask a question,
"Why Belgium, the No. 2 country in terms of the reactor density per area in the world (Table 2), showed a decreasing cancer mortality rates in the figure below?"
I don't know. However, at least as for thyroid cancer, the country must be worried. In a recent study (Bollaerts et al., 2014), Belgian people living in the vicinity (20 km radius) of 3 nuclear sites (out of total 5 sites studied) have shown to have 15-47% more chance of getting thyroid cancer than the people living outside the radius. If the study has taken accounted for sex-specific incidence rates, female thyroid cancer rates might have been higher, I suspect.

Table 2. Reactors in operation, in long term shutdown, or under construction (as of December 31, 2013)